This invention relates to catalysts, and, in particular, to catalyst materials wherein a metallic catalyst is supported on a substrate.
Catalysts are substances that accelerate chemical reactions, but are neither changed nor consumed by the reactions. Catalysts are used in a wide variety of chemical processes to obtain commercially viable rates for reactions that otherwise occur very slowly. Because the catalysts are not themselves reactants in the sense that they enter into the reaction, a relatively small amount of the catalyst is typically required.
In many cases, the catalysts promote the chemical reaction by providing a surface location at which the reactants can interact to effect the reaction. Catalysts are therefore typically provided in a finely divided form or a form having a large surface area per unit volume or weight, such as powder or sponge, to maximize the number of surface sites available to promote the reaction. The use of finely divided catalyst materials also promotes the most economical use of the catalyst, an important consideration because many catalysts are expensive to obtain or produce.
In one approach to attaining a large amount of catalyst surface area, atoms of the catalyst material are deposited upon a support surface called a substrate. The catalyst atoms are distributed over the surface of the substrate, so that little of the expensive catalyst material is present at any location other than the active surface. Maximum use is thereby attained of an available amount of the catalyst metal.
In one form of this approach, the substrate material is itself provided as small pellets or granules of a substance inert in the chemical reaction to be catalyzed, and the catalyst metal is coated upon the surface of the pellets. The coated pellets are readily fabricated, as by chemical deposition, and can be used as necessary. The reactants in the chemical reaction to be catalyzed are often in a gaseous or liquid stream, which can pass freely through a bed of the coated pellets. The coated pellets can be heated if elevated temperature catalysis is required, and can be cleaned as necessary.
In a particular chemical reaction of interest, carbon monoxide and oxygen are reacted together in the presence of a platinum catalyst, to form carbon dioxide. This catalyzed regeneration of carbon dioxide is of importance in certain types of carbon dioxide lasers, wherein the carbon dioxide is dissociated in carbon monoxide and oxygen in a high electric field in a closed system. The carbon dioxide must be regenerated by reaction of the carbon monoxide and oxygen, or the laser would soon become inoperative due to a deficiency of available carbon dioxide. However, the carbon monoxide and oxygen do not spontaneously react at a sufficiently high rate to regenerate carbon dioxide fast enough to replace that used up in the dissociation, in the absence of assistance, and therefore a platinum catalyst is provided to accelerate the regeneration reaction. Using such a catalyzed regeneration reaction, transverse electrode atmospheric lasers can be made to operate with some efficiency.
In this application of catalysis, the platinum catalysis metal may be supported on an aluminum oxide (alumina) substrate provided as fine pellets having a diameter of about 1/8 inch. The coated pellets are prepared by chemically depositing platinum atoms onto the surface of aluminum oxide pellets from a platinum-containing solution. The platinum is typically provided in an amount such that about 10-15 atomic percent of the final coated pellet is platinum.
The catalysis of the carbon dioxide regeneration reaction by platinum catalyst atoms coated onto alumina substrate pellets permits operation of the carbon dioxide laser. But, as with many catalyzed processes, a higher reaction rate would be desirable to achieve more chemical reaction product with reduced size and weight of the apparatus devoted to the regeneration processing.
There therefore exits a continuing need for an improved catalyst material for use in catalyzing reactions of many types. The catalyst material should promote increased reaction throughput, desirably with reduced usage of expensive catalysts. The present invention fulfills this need, and further provides related advantages.